The present invention relates to fluid fittings for connection to tubes and pipes by swaging and, more particularly, to a fitting having an axially movable swaging ring.
Fittings are commonly used to connect metal tubes and pipes to each other for use in a variety of applications, such as in the aerospace industry, to convey fuel, hydraulic control fluids and the like in an aircraft or space vehicle. In these applications, it is critical that there be a secure connection between the fitting and the tubes in order to withstand vibration and other adverse conditions without failure.
Various fittings have been developed in the past to connect tubes to each other. In one type of fitting, a radial swaging force is applied to the fitting and the tube, which may be done externally around the fitting or internally within the tube. In either case, the radial swaging force is applied directly to the fitting and tube by the tool. In some instances, the inner surface of the fitting has a plurality of axially spaced annular grooves into which the material of the tube is deformed by the swaging tool to make the swaged connection. In other instances, a curved or irregular configuration on the outer surface of the fitting is transferred to the inner surface of the fitting upon swaging, which causes the tube to deflect and conform to the irregular configuration and thereby make the connection.
Another type of fitting comprises a cylindrical sleeve having a tapered outer surface and a cylindrical inner surface for receiving a tube. A deforming ring surrounds the sleeve and has a tapered inner surface which matches and engages with the tapered outer surface of the sleeve. Before swaging, the deforming ring is positioned outwardly with respect to the sleeve such that no radial force is applied by the deforming ring to the sleeve. During swaging, the deforming ring is moved axially in a forward direction over the sleeve such that the interaction of the tapered surfaces on the ring and the sleeve applies a radial force deforming the sleeve and the tube inwardly to make a swaged connection between them. These fittings shall be generally referred to as axially swaged fittings.
In the aircraft industry and in the marine and commercial fields, it is desirable to have the weight of the hydraulic plumbing installation as low as possible. All of the fittings described above pose a problem in this regard, since many hundreds of them are used in an aircraft, thus making their total weight contribution a noticeable amount. Because of the high flexure and operating pressures in the tubes, the fittings are made of metal and generally must be sufficiently large in both size and weight to resist fatigue failure and to ensure adequate holding power and tube retention capability. As a result, most fittings in use today are relatively large and heavy and, therefore, add undesirable weight to the aircraft. Since axially swaged fittings have a deforming ring, which remains as a permanent part of the swaged fitting, these fittings tend to add extra undesirable weight.
Another problem which especially concerns axially swaged fittings is the inability to conveniently hold the deforming ring onto the sleeve prior to swaging, and then to securely lock the ring to the sleeve after swaging. In some instances, the deforming ring is preassembled onto the sleeve and held there by frictional engagement or other means. However, if the frictional engagement is insufficient, the deforming ring may become separated from the sleeve and sometimes lost or damaged. If the frictional engagement is too great, however, the outer end of the sleeve may be radially pre-deformed to such an extent that the tubing will not fit within the radially constricted sleeve. In other instances, the deforming ring is simply loosely packaged with the sleeve and subject to loss or damage or, even worse, the ring may be incorrectly installed when placed over the sleeve.
Accordingly, there has existed a definite need for an axially swaged fitting that is smaller in size and lighter in weight than the known fittings, while still maintaining a high tube retention capability. There has further existed a definite need for an axially swaged fitting in which the deforming ring is securely attached to the swaging sleeve prior to swaging, without permanently deforming the sleeve's tube insertion diameter, and in which the ring is positively locked to the sleeve after swaging. The present invention satisfies these and other needs and provides further related advantages.